<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
<div id="app">
  <h1>当前计数：{{counter}}</h1>
  <button @click="add">+</button>
  <button @click="sub">-</button>
</div>

<script src="../js/vue.js"></script>
<script>
  const app = new Vue({
    el: '#app',
    data: {
      counter: 0
    },
    methods: {
      add: function () {
        console.log('add被执行'),
            this.counter++
      },
      sub: function () {
        console.log('sub被执行'),
            this.counter--
      }
    }
  })
</script>
</body>
</html>